Inverse Gas Chromatography Analysis Research Articles

Application of inverse gas chromatography to bench scale flotation of sulphide ore

ABSTRACT Inverse gas chromatography (IGC) is receiving increasing attention due to its high precision and ease of application in determining various characteristics of a wide variety of materials of different shapes and morphologies. This study details an experimental investigation into the application of the IGC technique to the flotation of sulphide minerals. Rather than giving the surface energy, the trends associated with the various concentrates and tailings are described. Bench-scale flotation experiments of a nickel-copper sulphide ore were conducted in a Denver flotation cell. The IGC analyses were carried out on the timed concentrates, as well as on the final tailings, in order to evaluate the correlation between surface energetics and the flotation response of the ore particles. The results indicated that the floatability of the concentrates was directly related to the surface energy of the particles. Both dispersive and specific components of surface free energy increased by increasing the necessary time for the particles to be floated, which was consistent with the obtained values for the work of adhesion to water. However, the flotation response of the tailings was not consistent with the expectations from the surface energy value. The significance of the sample composition, particle size distribution, and their consequences in surface energy-flotation response relationship were also observed.

Evaluation of Time Consolidation Effect of Pharmaceutical Powders.

We aim to perform a systematic study of the time consolidation effect, i.e. the reduction of powder flowability resulting from at-rest storage, on a diverse array of pharmaceutical powders under different stress, humidity, and length of time. A ring shear cell-based methodology was employed. An instantaneous flow function was obtained, followed immediately by at-rest consolidation at precisely controlled humidity, stress, and duration. The consolidated powder was then subjected to shear-cell measurement. The difference in flowability between the immediate and consolidated specimens were attributed to the time consolidation effect. Among the six excipients tested, three exhibited time consolidation at varying extents. Citric acid and starch underwent time consolidation only at high relative humidity (RH = 75%), promoted by vapor condensation and liquid bridge formation. For both materials, the flowability decreased with time, and the extent of time consolidation was not sensitive to the stress applied (0.4-2kPa). Importantly, mannitol was found to time consolidate under both 50% and 75% RH. Given time, mannitol formed cake, giving rise to flow function below unity. Inverse gas chromatography analysis indicated that mannitol possesses high total surface energy among known pharmaceutical powders. While time consolidation is prevalent among pharmaceutical powders, most can be mitigated by controlling the RH to below 75%. Notably, for materials possessing high surface energy, such as mannitol, time consolidation could occur at ambient humidity. Therefore, it is desirable to consider in-depth time consolidation evaluation for high surface energy powders, e.g. those subjected to milling or of amorphous nature.

Infiltration of direct-spun carbon nanotube articles

A key step towards realizing the promise of macroscopic carbon nanotube (CNT) articles in high-performance structural applications is polymer infiltration into the porous CNT structure, which improves stress transfer and promotes long-term material integrity. However, infiltration is often found to be sub-optimal - a significant impediment to the scaling and adoption of CNT-article composites that has thus far received little systematic attention. In this study, a unique combination of inverse gas chromatography (IGC) and a statistical thermodynamic model is used to accurately quantify the energetic driving force for infiltration into CNT articles for the first time. This is measured to have a very low value. Using gas chromatography-mass spectroscopy, IGC analysis and electron microscopy, this low energy is found to result from near-complete surface coverage by non-graphitic pyrolysis byproducts. The surface energy is improved by plasma treatment as confirmed by IGC analysis. The effects of the surface treatment and modifications to the porous structure on the infiltration rate of model liquids are studied by optical imaging. Accurate surface energy measurements and image analysis are coupled to shed light on the critical parameters in these CNT articles that dictate the infiltration physics, which can be tuned to maximize the rate and extent of space filling.

Removal of Safranine T by a highly efficient adsorbent (Cotinus Coggygria leaves): Isotherms, kinetics, thermodynamics, and surface properties

Leaf-based adsorbents have attracted many researchers due to their low cost, high efficiency, and high adsorption capacity. In the present study, the performance of Cotinus Coggygria leaves on the adsorptive removal of Safranine T dye from an aqueous solution was investigated. Before the adsorption studies, the inverse gas chromatography (IGC) method was performed to observe the surface properties of Cotinus Coggygria, for the first time. With the data obtained from IGC analysis, the acidity/basicity degree of the adsorbent surface and the required conditions for the highest adsorption capacity were determined. The surface of the leaves was found to have a basic characteristic. The adsorption studies were carried out under different parameters including contact time, temperature, pH, initial dye concentration, and adsorbent dosage. The maximum percentage of Safranine T was obtained as 93.62% at pH = 7 and 55 °C. The different isotherms were applied namely Langmuir, Freundlich, D-R, Harkins-Jura, and Temkin isotherm models. From the correlation coefficients, it was obtained that the adsorption took place in agreement with the Langmuir isotherm. The adsorption capacity showed the maximum at 2000 mg/g in pH = 7 at 55 °C. As a result of the kinetic studies, it was seen that adsorption followed the pseudo-second-order kinetic model. When thermodynamic parameters were obtained, it was seen that the adsorption occurred exothermically and spontaneously. This study suggests that Cotinus Coggygria leaves are highly efficient biobased materials as an adsorbent.

Probing Surface Characteristics of Rare Earth Minerals Using Contact Angle Measurements, Atomic Force Microscopy, and Inverse Gas Chromatography.

Rare earth minerals (REMs) such as bastnaesite, monazite, and xenotime are of considerable significance since they are the main commercial sources for rare earth elements (REEs) with cutting-edge applications. Fundamental understanding of surface properties of REMs is essential to identify the reactions taking place at different interfaces to develop more robust technologies for the recovery of REEs. The goal of this study is to provide a comprehensive investigation on the surface energy characteristics of bastnaesite and xenotime, as the primary sources of light and heavy rare earth elements, respectively. Crystal’s orientation of REMs was identified using surface X-ray diffraction analysis, whereas the morphology and elemental composition were characterized using scanning electron microscopy and energy dispersive spectra analyses. Wettability of REMs was studied using sessile drop contact angle measurement technique, and the surface energy and its constituents were evaluated using Fowkes, van Oss–Chaudhury–Good, Owens–Wendt–Rabel–Kaelble, Zisman, and Neumann models. Atomic force microscopy (AFM) was used to compare the local surface properties and work of adhesion of REMs by analyzing the force profile between the mineral surfaces and a n-type silicon tip. Inverse gas chromatography (IGC) was employed to study the surface energy heterogeneity of REM powders and evaluate the dispersive and Lewis acid–base interactions. Results indicated that the dispersion forces have a larger contribution to the surface energy of both REMs in comparison with the polar interactions. The surface energy values obtained using contact angle measurements were lower than those obtained using IGC, however, the IGC results seemed to be closer to reality since the contact angle results showed a strong dependence on probe liquids, roughness, and local properties of the surfaces. Contact angle measurements and AFM analysis indicated that bastnaesite had higher hydrophobic character, whereas the IGC analysis revealed that the surface energy of xenotime was lower than that of bastnaesite at higher surface coverages. Despite the shortcomings of each method, results showed that a combination of these techniques could provide a deeper understanding of surface energy and wetting behavior of minerals.

Surface energy of air fractionated corn stover

Despite decades of research, Integrated Biorefineries (IBRs) are still not commercially viable because of the long-standing, unresolved challenges related to biomass solids handling and transport (e.g., flowability and fouling), and pretreatment e.g., wettability and conversion). The compendium of challenges facing IBRs lead to operational reliability and time-on-stream estimates of 30%, yet economically viable IBRs require greater than 90% operational reliabilities. The performance of commercial solids handling operations is largely dependent on the fundamental thermodynamic property, surface energy. Combining surface area, thermogravimetric, and inverse gas chromatography analyses, we show the observed differences in surface energy (e.g., wettability and work of cohesion) for anatomically air fractionated corn (Zea mays L.) stover. This study highlights the importance of understanding and tuning biomass surface energy to improve IBR solids handling and transport, and pretreatment operations.

A novel colored talc filler: Preparation and surface property determination using two distinct methods

A better understanding of filler's surface properties is critical for determining the most effective polymer reinforcement fillers. In this work, a colored talc filler (CTF) was prepared and its surface properties were comparatively studied to those of talc filler (TF), using inverse gas chromatography (IGC) and contact angle methods—Owens–Wendt–Kaelble (OWK), van Oss–Chaudhury–Good (vOCG) and Wu. The results indicated that the dispersive component (γSD) for both samples contributed a major part (68–81%) of the total surface energy (γST), and displayed a decreasing trend with increasing surface coverage, meaning the fairly energetic surface heterogeneity for them. The γSD values determined by the contact angle methods were consistent, although lower than those using IGC analysis. The specific component (γSSP) calculated by the contact angle methods were also consistent and lower than those calculated using IGC. The specific Gibbs free energies of adsorption (ΔGsp) changed with surface coverages, further confirming the heterogeneous nature of both samples. The significantly lower γST value for CTF could reduce filler particle-particle interactions, allowing a better dispersion in matrix, and thus lead to an improvement in mechanical performance of CTF/polymer composite.

Study on the surface properties of colored talc filler (CTF) and mechanical performance of CTF/acrylonitrile-butadiene-styrene composite

In this work, a novel colored talc filler (CTF) was prepared, and its surface properties were subsequently studied and compared to those of talc filler (TF) using inverse gas chromatography (IGC) and contact angle measurement. The mechanical properties of acrylonitrile-butadiene-styrene (ABS) composites filled with CTF and TF were investigated as well. The results indicated that the dispersive component (γSD) for both samples contributed the major part of the total surface energy (γST). The values determined by the contact angle methods were consistent, although lower than those using IGC analysis. Compared to γSD, the polar component (γSSP) contributed less to γST, implying a lower polarity for both samples. The γSSP values calculated by the contact angle methods were also consistent and lower than those calculated using IGC. The lower γST value for CTF could reduce filler particle-particle interactions, allowing a better dispersion in ABS matrix, and thus leading to an increase in ABS/CTF composite performance.

Investigating High-Concentration Monoclonal Antibody Powder Suspension in Nonaqueous Suspension Vehicles for Subcutaneous Injection

Developing high-concentration monoclonal antibody (mAb) liquid formulations for subcutaneous (s.c.) administration is challenging because increased viscosity makes injection difficult. To overcome this obstacle, we investigated a nonaqueous powder suspension approach. Three IgG1 mAbs were spray dried and suspended at different concentrations in Miglyol® 840, benzyl benzoate, or ethyl lactate. Suspensions were characterized for viscosity, particle size, and syringeability; physical stability was visually inspected. Suspensions generally outperformed liquid solutions for injectability despite higher viscosity at the same mAb concentrations. Powder formulations and properties had little effect on viscosity or injectability. Ethyl lactate suspensions had lowest viscosity (<20 cP) and lowest syringe injection glide force (<15 N) at mAb concentrations as high as 333 mg/mL (500 mg powder/mL). Inverse gas chromatography analysis indicated that the vehicle was the most important factor impacting suspension performance. Ethyl lactate rendered greater heat of sorption (suggesting strong particle-suspension vehicle interaction may reduce particle-particle self-association, leading to low suspension viscosity and glide force) but lacked the physical suspension stability exhibited by the other vehicles. Specific mixtures of ethyl lactate and Miglyol® 840 improved overall performance in high mAb concentration suspensions. This study demonstrated the viability of high mAb concentration (>300 mg/mL) in suspension formulations for s.c. administration.

Surface energetics of cementitious materials and their wettability by an epoxy adhesive

The surface thermodynamic properties of cementitious materials and the wettability of these substrates by an epoxy adhesive were investigated using various surface analysis techniques. In a first step, surface energies of hardened cement pastes were assessed either by contact angle measurements using the Owens and Wendt approach, or by inverse gas chromatography (IGC). A good correspondence was found between the two techniques for the dispersion contribution γ s d , and a strong amphoteric behavior of these materials was also demonstrated. Additionally, a surface carbonaceous contamination detected by X-ray photoelectron spectroscopy (XPS) was found to lower the surface energy of as-received samples, whereas an acetone cleaning treatment resulted in increased γ s d values. In a second part, surface characterizations were performed on three synthetic compounds, representative of the main hydration products of hardened cement pastes, i.e. calcium hydroxide, ettringite and calcium silicate hydrate (C -S -H). IGC experiments provided γ s d values ranging from 45.6 up to 96.3 mJ m −2 at 35 °C, and the acid–base behavior was correlated to the water content. Last, XPS and IGC analyses were performed on cement paste powders coated either with an epoxy resin (R) or with an amine hardener (H), separately, at mass loadings up to 10 wt.%. Changes in the dispersion contribution to the surface energy ( γ s d ) and Lewis acid–base interaction energy were found to be significantly dependent on the adsorption of both H and R, showing a substantial wetting of the mineral substrate by the adhesive components. In addition, XPS evidenced interfacial hydrogen bonding between the hardener and the cementitious substrates.

Predicting the aerosol performance of dry powder inhalation formulations by interparticulate interaction analysis using inverse gas chromatography

Previous studies have demonstrated the utility of inverse gas chromatography (IGC) in discriminating the differences in surface energy between salmeterol xinafoate (SX) powders prepared by conventional sequential batch crystallization and micronization and by supercritical fluid crystallization. In the present study, solubility parameters derived from IGC analysis at infinite dilution (zero coverage) were further utilized to evaluate the influence of solid-solid interactions on the in vitro aerosol performance of these SX samples, with or without the inclusion of a lactose carrier. To this end, the strength of cohesive SX-SX interactions and that of adhesive SX-lactose interactions were computed for the samples from the corresponding solubility parameters, and their fine particle fractions determined using a multi-stage liquid impinger. It was found that the aerosol performance of SX could be substantially improved by the addition of lactose carrier only if the adhesive SX-lactose interactions were stronger than the cohesive SX-SX interactions. The difference in strength between these two forms of interactions also displayed a significant correlation with the increase in fine particle fraction after the addition of lactose carrier. These results suggest that IGC-based interparticulate interaction measurements may serve as a useful means for predicting the aerosol performance of dry powder inhalation formulations.

Surface characterization of salmeterol xinafoate powders by inverse gas chromatography at finite coverage

In our previous studies, surface analysis by inverse gas chromatography (IGC) at infinite dilution (zero coverage) was performed on four salmeterol xinafoate (SX) powdered samples, viz, two supercritical CO2‐processed Form I (SX‐I) and Form II (SX‐II) polymorphs, a commercial granulated SX (GSX) raw material and its micronized product (MSX). Both GSX and MSX are also of the same Form I polymorph. To further probe the differences in surface properties between the samples, the present study has extended the IGC analysis to the finite concentration range of selected energy probes. The adsorption isotherms of the SX samples were constructed using (nonpolar) octane, (polar acidic) chloroform, and (polar basic) tetrahydrofuran as liquid probes. Type II adsorption isotherms with weak knees were observed with each probe for all SX Form I samples. The extents of probe adsorption by the samples at various relative pressures follow the rank order: SX‐II > GSX ≈ MSX > SX‐I, indicating that the SX‐I has fewer high‐energy adsorption sites than GSX and MSX. Type III isotherms were observed for SX‐II with the two polar probes, indicative of weak adsorbate–adsorbent interactions. The additional information generated shows that IGC analysis at finite coverage is a valuable complementary tool to that at infinite dilution. © 2005 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:695–700, 2005

The effective surface energy of heterogeneous solids measured by inverse gas chromatography at infinite dilution

Inverse gas chromatography (IGC) at infinite dilution has been widely used to access the nonspecific surface free energy of solid materials. Since most practical surfaces are heterogeneous, the effective surface energy given by IGC at infinite dilution is somehow averaged over the whole sample surface, but the rule of averaging has thus far not been established. To address this problem, infinite dilution IGC analysis was carried out on mixtures of known heterogeneity. These materials are obtained by mixing two types of solid particles with significantly different surface energies as characterized individually with IGC, and results are obtained for binary combinations in varying proportions. It is found that when all surface components have the same accessibility by probe molecules, the effective surface energy of such a heterogeneous surface is related to the surface energy distribution by a square root linear relationship, σ eff LW =∑ iφ i σ i LW , where σ i LW refers to the nonspecific (Lifshitz–van der Waals) surface energy of patches i, and φ i to their area fraction.

Effects of dehydration on the apolar surface energetics of inorganic paper fillers

The surface energies of various inorganic fillers including kaolin clay, titanium dioxide, and talc were examined using inverse gas chromatography (IGC). In an earlier investigation that examined calcium carbonate fillers, dehydration by heating under a dry nitrogen purge had a substantial influence on the apolar ( γ LW S) and polar ( γ AB S) components of surface energy as measured using IGC. Using the same approach, the influence of such conditioning on several inorganic fillers used in papermaking were determined using preconditioning IGC from 100 to 300 °C, and sequential isothermal analysis at 100 °C. Results from IGC analysis of titanium dioxides (rutile and anatase) were similar to precipitated calcium carbonate (PCC) for temperatures up to 200 °C. PCC was significantly more energetic after preconditioning at 300 °C, which may indicate the onset of significant thermal decomposition that titanium dioxides will not exhibit. Kaolin clay samples had relatively high apolar surface energy similar to that of the chalk samples. Calcination gave lower γ LW S values that could not be accounted for by changes in the microporous structure. More likely the differences resulted from contamination of highly energetic surface sites with adsorbates other than water. Talc samples exhibited relatively high apolar surface energies that increased with preconditioning temperature. The results provided insight into the significance of water on the final adhesion properties of fillers in the sheet structure or coating layer.

Phase Segregation in SAN/PMMA Blends Probed by Rheology, Microscopy, and Inverse Gas Chromatography Techniques

Phase segregation in the poly(styrene-co-acrylonitrile)/poly(methyl methacrylate) (SAN/PMMA) blend with lower critical solution temperature (LCST) was assessed by linear viscoelastic rheology, optical microscopy, and inverse gas chromatography (IGC) techniques for various blend compositions. At low temperatures, the blends showed a classical behavior of homogeneous polymer melts, whereas in the vicinity of phase segregation, a shoulder in the storage modulus and in the linear relaxation modulus G(t) was observed. The width of such a low-frequency/longer-time plateau and the terminal relaxation time were found to increase with temperature. Such a behavior was attributed to variable morphologies appearing at different temperatures. The development of the morphology was found to take place within a given interval of temperature rather than at a single critical temperature. Optical microscopy and IGC analyses supported the observed peculiar behavior of such a blend. Time−temperature superposition, origin of elasticity, and the Fredrickson and Larson theory were discussed in light of the obtained results.

Acid–base characterization of wood and selected thermoplastics

The objective of this work was to study the acid–base properties of wood, poly(vinyl chloride) (PVC), nylon 6 and 6,6 by wetting and inverse gas chromatography (IGC) analyses. Information about the acid–base characteristics of these materials should be useful to improve the intermolecular bonding properties in wood-plastic composites. The acid–base properties of pine wood veneers, PVC and nylon 6,6 were determined by contact angle analysis using the work of adhesion (or Fowkes), van Oss–Chaudhury–Good (vOCG) and Chang–Qin–Chen (CQC) approaches. The IGC analysis was performed on maple wood, PVC and nylon 6 particles, and was carried out at infinite dilution using a series of both non-polar and polar acid–base probe gases. The contact angle analysis of the wood veneers using both the work of adhesion and the vOCG approaches showed that the presence of wood extractives was the dominant factor influencing the acid–base properties of the veneers. Particularly, it was shown that aging of non-extracted veneers increased and decreased their acidic and basic properties, respectively. This is presumably due to reorientation of functional groups and oxidation at the wood extractives–air interface. In the vOCG model, considerably higher base/acid ratios were obtained when using probe liquid parameters according to van Oss compared to those obtained by using liquid parameters according to Della Volpe and Siboni. Based on both the vOCG and the CQC models it was shown that nylon 6,6 had greater acid and base parameters than PVC. Additionally, the CQC model seems to be a promising tool to determine the acid–base characteristics of materials. The IGC analysis showed that nylon 6 had greater acid and base parameters than both wood and PVC which implies a strong ability to enter into acid–base interactions. The results also suggested that an increase in the basic character of wood could have the potential to improve its bonding with both PVC and nylon 6.

Model Compound Vulcanization And IGC As Prediction Tools In Carbon Black Effect On Vulcanization

AbstractThe influence of carbon black (CB) in a rubber formulation can be observed during the vulcanization process. However, looking through literature there seems to be a lack of information related to the role of CBs in vulcanization reaction. The present work is focused on the application of Model Compound Vulcanization (MCV) approach and Inverse Gas Chromatography (IGC) to predict the role of carbon black on vulcanization.Squalene was chosen as the model molecule of natural rubber to undergo the vulcanization in the presence of carbon black. This methodology gives rise to several advantages. On one hand, the model allows following the accelerator, vulcanization intermediate compounds, and even the crosslinked model molecule. Moreover, the similarity between the model and the polymer chain allows further extrapolation to discover the real sample's performance. In order to complete the information required IGC analysis was used. IGC has been performed using both dispersive and specific probes to elucidate a wide range of CB surface active sites.The application of this prediction tool to special grades revealed different effects that have been verified with real formulations in both cases.

Surface characteristics of polyurethane adhesive formulations

The surface characteristics of a two-part polyurethane adhesive formulation, based on controlled amounts of polyol, isocyanate, and catalyst, have been studied by methods including contact angle analysis, 1R spectroscopy, and inverse gas chromatography (IGC). The response of surface properties to various cure regimes and to exposure to water has been established. IGC analyses show that the adhesive surface is mildly basic, and as first evaluated by contact angle methods, has a surface energy close to 40 mJ/m2. This is largely accounted for by dispersion forces. Following immersion in water at 60°C, however, the surface energies change, the most important effect being an increase in the non-dispersive component. FTIR spectra show that immersion in water also produces chemical changes in the surface region, likely related to enolization effects. On subsequent immersion of the adhesive surface in non-polar n-heptane, the non-dispersive component of the surface energy is again reduced, showing that surface re...